Don't attempt send failure notifications for deleted messages.

Fixes #2963

// FREEBIE

src/org/thoughtcrime/securesms/database/ThreadDatabase.java

@@ -22,6 +22,7 @@ import android.database.Cursor;
 import android.database.MergeCursor;
 import android.database.sqlite.SQLiteDatabase;
 import android.database.sqlite.SQLiteOpenHelper;
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 import android.util.Log;
 
@@ -371,7 +372,7 @@ public class ThreadDatabase extends Database {
     }
   }
 
-  public Recipients getRecipientsForThreadId(long threadId) {
+  public @Nullable Recipients getRecipientsForThreadId(long threadId) {
     SQLiteDatabase db = databaseHelper.getReadableDatabase();
     Cursor cursor     = null;
 

src/org/thoughtcrime/securesms/jobs/PushTextSendJob.java

@@ -92,8 +92,10 @@ public class PushTextSendJob extends PushSendJob implements InjectableType {
     long       threadId   = DatabaseFactory.getSmsDatabase(context).getThreadIdForMessage(messageId);
     Recipients recipients = DatabaseFactory.getThreadDatabase(context).getRecipientsForThreadId(threadId);
 
+    if (threadId != -1 && recipients != null) {
       MessageNotifier.notifyMessageDeliveryFailed(context, recipients, threadId);
     }
+  }
 
   private void deliver(MasterSecret masterSecret, SmsMessageRecord message)
       throws UntrustedIdentityException, InsecureFallbackApprovalException, RetryLaterException